A large number of wheeled structures or “vehicles” are used to transport a variety of different items both inside and outside of houses. They vary from simple transport trolleys e.g. in production facilities over logistics equipment to hospital beds. A person, who takes on the function as a human engine, manually pushes by far the larger proportion of these vehicles.
When transporting heavy objects on a vehicle, the person pushing is exposed to severe physical strain both to initiate movement, to control the movement and in order to brake the vehicle as and when desired. For this reason a number of “assistive drive technologies” have been developed. Typically, such technologies help the person pushing the vehicle by supplying the force needed to propel the vehicle either forwards or backwards. The person normally supplies the steering force, by pushing directly onto the vehicle or onto a steering handle supplied.
Most of the vehicles have four wheels placed in a rectangular formation in order to give the vehicle stability. If traction—as known from many assistive drive systems—is supplied by motorizing e.g. the two rear wheels of the vehicle, the vehicle will have a pattern of movement similar to that of a car, which means that the vehicle needs a lot of space to manoeuvre, turn around corners etc. More importantly, moving such a vehicle sideways will involve “kerb side parking”. Therefore, a number of assistive drive technologies have been developed, which supply force and traction to the drive surface via a fifth—often centre placed—wheel. These drive wheels, which are normally equipped with a reversible electric drive motor, are oriented in such a way that when the motor is activated they will supply the power needed in order to move the vehicle either forwards or backwards as desired. The advantage of such centre placed drive wheels is that the centre of the vehicle becomes the turning point of the vehicle, which again means that the vehicle requires less space to e.g. turn around a 90° corner.
Examples of such beds having a fifth centre placed driving wheel are disclosed in for example U.S. Pat. Nos. 6,877,572, 6,752,224, and 6,902,019.
However, the known centre placed assistive drive systems show a number of disadvantages, which the present invention overcomes, the most important ones being:                As drive force is supplied only “along ships”, the known systems do not help move the vehicles sideways. Actually, they may in some instances work against such movements.        As the weight of the vehicle, even in its unloaded condition—for stability reasons—predominantly is carried by the four wheels in rectangular formation, it often becomes difficult for the drive wheel to obtain sufficient traction to move the vehicle when heavily loaded and/or when moving on an uneven drive surface.        